Mosquito-bacteria interactions during larval development trigger metabolic changes with carry-over effects on adult fitness

In animals with distinct life stages such as holometabolous insects, adult
phenotypic variation is often shaped by the environment of immature
stages, including their interactions with microbes colonizing larval
habitats. Such carry-over effects were previously observed for several
adult traits of the mosquito Aedes aegypti after larval exposure to
different bacteria, but the mechanistic underpinnings are unknown. Here,
we investigated the molecular changes triggered by gnotobiotic larval
exposure to different bacteria in Ae. aegypti. We initially screened a
panel of 16 bacterial isolates from natural mosquito breeding sites to
determine their ability to influence adult life-history traits. We
subsequently focused on four bacterial isolates (belonging to
Flavobacterium, Lysobacter, Paenibacillus, and Enterobacteriaceae) with
significant carry-over effects on adult survival and found that they were
associated with distinct transcriptomic profiles throughout mosquito
development. Moreover, we detected carry-over effects at the level of gene
expression for the Flavobacterium and Paenibacillus isolates. The most
prominent transcriptomic changes in gnotobiotic larvae reflected a
profound remodeling of lipid metabolism, which translated into phenotypic
differences in lipid storage and starvation resistance at the adult stage.
Together, our findings indicate that larval exposure to environmental
bacteria trigger substantial physiological changes that impact adult
fitness, uncovering a possible mechanism underlying carry-over effects of
mosquito-bacteria interactions during larval development.